Wireless communication systems have been extremely popular for more than a decade. They allow users to communicate with each other while remaining geographically mobile. In addition, these systems allow communications to be in different modes, such as full-duplex voice, half-duplex voice, and data, as examples. An example of a wireless communication system protocol is 1xEV-DV which specifies requirements for a system optimized for data and voice communications. Although an 1xEV-DV wireless communication system serves to exemplify the invention, it shall be understood that the invention is applicable to other types of wireless communication systems.
FIG. 1 illustrates a block diagram of an exemplary wireless communication system 100. The wireless communication system 100 comprises a network 102, and a plurality of base stations 104 and 106 communicatively coupled to the network 102. The wireless communication system 100 serves a plurality of subscriber units (SUs), two of which are shown as SUs 108 and 110 currently communicating with base station 104, and one of which is shown as SU 112 currently communicating with base station 106. The network 102 includes a plurality of network devices that provide data communication services to the SUs. The base stations 104 and 106 provide an air interface between the network 102 and the SUs.
In the case of wireless communication system 100 operating in compliance with the 1xEV-DV protocol, the base stations 104 and 106 communicate with the SUs 108, 110, and 112 using a code division multiple access (CDMA) air interface. In CDMA, Walsh codes are used to define channels through which communications are sent from base stations to SUs. In the 1xEV-DV protocol, there are 28 Walsh codes of length 32. In addition, the 1xEV-DV protocol is backward compatible with the IS-95 protocol, which has 55 Walsh codes of length 64 reserved for traffic channels in the forward link used by base stations to communicate with SUs.
FIG. 2 illustrates a block diagram of an exemplary base station 200. The base station 200 comprises a source 202 for the Pilot channel, a source 204 for the Paging channels, a source 206 for the Sync channel, and a source 208 for the traffic channels. The base station 200 further comprises a plurality of digital processing sections (e.g., coding, interleaving, etc.) 210, 212, 214, and 216 for processing the Pilot, Paging, Sync, and Traffic information, respectively. The base station 200 further comprises a plurality of modulo-2 adders 218, 220, 222, and 224 including inputs respectively coupled to the outputs of digital processing sections 210, 212, 214, and 216, and other inputs to respectively receive Walsh codes WUn, WVn, WYn, and WZn. The base station 200 further comprises a summer 226 including inputs respectively coupled to the outputs of the modulo-2 adders 218, 220, 222, and 224.
The base station 200 further comprises an I- and Q-modulator including a pair of I- and Q-mixers 228 and 230 having respective inputs coupled to the output of the summer 226, and other inputs to respectively receive pseudo-random (PN) I- and Q-sequences, baseband processing units 232 and 234 including inputs respectively coupled to the outputs of the mixers 228 and 230, and a second summer 236 having inputs respectively coupled to the outputs of the baseband processing units 232 and 234. Additionally, the base station 200 further comprises an up-converter 238 coupled to the output of the second summer 236. The base station 200 further includes an antenna 240 coupled to the output of the up-converter 238.
FIG. 3 illustrates a diagram of a Walsh code tree 300 in accordance with the IS-95 and 1xEV-DV protocols. As discussed above, an IS-95 compliant system uses 64 Walsh codes of length 64 (i.e. Wi64) to define channels for base stations to communicate with SUs in the forward link. According to the protocol, the first Walsh code W064 is reserved for the Pilot channel (i.e., WUn=W064), the second through eighth Walsh codes W164-W764 are reserved for Paging channels (i.e., WVn=W164-W764), and the 32nd Walsh Code W3264 is reserved for the Sync channel (i.e., WYn=W3264). A 1xEV-DV wireless communications system uses the 32-length Walsh codes Wk32 which forms the basis for the 64-length Walsh codes Wi64.
In general, the use of a 64-length Walsh code eliminates the 32-length Walsh code which it is derived from. Accordingly, the use of the first and second 64-length Walsh codes W064 and W164 for the Pilot channel and the first Paging channel eliminates the first 32-length Walsh code W032 for use as a traffic channel in a 1xEV-DV compliant system. The use of the next six 64-length Walsh codes W264-W764 for the remaining Paging channels eliminates the second through fourth 32-length Walsh code W132-W332 for use as traffic channels in a 1xEV-DV compliant system. The use of the 32nd 64-length Walsh code W3264 for the Sync channel eliminates the 16th 32-length Walsh code W1632 for use as a traffic channel in a 1xEV-DV compliant system.
Accordingly, the way the Walsh code tree 300 is configured results in an inefficient use of channel resources and a relatively complicated algorithm implemented by a base station to assign a traffic channel to communicate with an SU. For instance, the nine 64-length Walsh codes used for the Pilot, Paging, and Sync channels eliminates 5 of the 32-length Walsh codes for use as traffic channels in a 1xEV-DV compliant system. In addition, because the Sync channel is assigned to the middle of the Walsh code tree 300, this creates discontinuous Walsh code sections for traffic channel use, which makes it more complicated for a base station to assign a traffic channel.